How do you measure and classify angles? When two rays meet at a point In plane geometry, they form an angle at that common endpoint, called the vertex of the angle. Angles lie in a plane, but this plane does not have to be a Euclidean plane. There are a variety of different types of angles. These types include straight, right, acute or obtuse. These are a portion of the total circle that 360˚. A straight angle is the same as half the circle and is 180° whereas a right angle is a quarter of a circle and is 90°. All these can be measured using a protractor in the geometry box, that is shaped like a capital D.

You will definitely need a protractor for these worksheets and lessons. The lesson walks you step-by-step through measuring the angles by matching them arms up on the protractor. Once you know the measure of the angle we classify the angles. Straight angles are basically straight lines and have a measure of 180 degrees. Right angles measure 90 degrees. Acute angles are less than 90 degrees. Obtuse angles are the goldilocks of angles; they measure between 90 and 180 degrees. Reflex angles get a bit extreme and measure between 180 and 360 degrees. These worksheets explain how to classify angles as straight, right, acute, obtuse, or reflex. The different angle classifications are defined for students.